Quantal secretion at frog cutaneous pectoris neuromuscular junctions will be stimulated by various agents, and the amplitude and rate of occurrence of miniature endplate potentials (mepps) will be measured with a modified procedure of fluctuation analysis. This procedure uses the power spectrum of the fluctuations in membrane potential at the endplate together with the second (variance), third (skew) and fourth semi-variants of the fluctuations to compute the mepp parameters. Its results are insensitive to drifting membrane potential, nonlinear summation of mepps and nonstationary rates of occurrence, and they allow changes in the mepp amplitude distribution to be monitored and corrected for. This procedure will also be used to measure the amplitude and rate of occurrence of miniature endplate currents (mepcs) at voltage-clamped lizard or mouse neuromuscular junctions. The ultrastructure of the nerve terminals and their uptake of horseradish peroxidase will be examined in the electron microscope. The junctions will be stimulated by black widow spider venom, La3+, K+-rich solutions, or hypertonic solutions, and the effects of low temperature (1-2 degrees C) and inhibitors of acetylcholine synthesis (hemicholinium-3 or Na+-free, Li+ substituted solutions on the quantal secretion induced by these agents will be tested. The morphologic and electrophysiologic results will be used to characterize the recycling processes which sustain the population of synaptic vesicles and maintain the quantal stores of acetylcholine in the nerve terminals. These recycling processes support the long term function of a synapse, and their malfunction will impair transmission and produce diseased states in an organism.